Reserve box/unbox/equals/hashCode methods inside inline classes

#KT-26573 Fixed

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -330,6 +330,7 @@ public interface Errors {
     DiagnosticFactory0<PsiElement> INLINE_CLASS_CANNOT_IMPLEMENT_INTERFACE_BY_DELEGATION = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<KtTypeReference> INLINE_CLASS_CANNOT_EXTEND_CLASSES = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<KtTypeReference> INLINE_CLASS_CANNOT_BE_RECURSIVE = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory1<PsiElement, String> RESERVED_MEMBER_INSIDE_INLINE_CLASS = DiagnosticFactory1.create(ERROR);
 
     // Secondary constructors
 

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -661,6 +661,7 @@ public class DefaultErrorMessages {
         MAP.put(INLINE_CLASS_CANNOT_IMPLEMENT_INTERFACE_BY_DELEGATION, "Inline class cannot implement an interface by delegation");
         MAP.put(INLINE_CLASS_CANNOT_EXTEND_CLASSES, "Inline class cannot extend classes");
         MAP.put(INLINE_CLASS_CANNOT_BE_RECURSIVE, "Inline class cannot be recursive");
+        MAP.put(RESERVED_MEMBER_INSIDE_INLINE_CLASS, "Member with the name ''{0}'' is reserved for future releases", STRING);
 
         MAP.put(VARIANCE_ON_TYPE_PARAMETER_NOT_ALLOWED, "Variance annotations are only allowed for type parameters of classes and interfaces");
         MAP.put(BOUND_ON_TYPE_ALIAS_PARAMETER_NOT_ALLOWED, "Bounds are not allowed on type alias parameters");

compiler/frontend/src/org/jetbrains/kotlin/resolve/TargetPlatform.kt

@@ -119,7 +119,8 @@ private val DEFAULT_DECLARATION_CHECKERS = listOf(
     SuspendOperatorsCheckers,
     InlineClassDeclarationChecker,
     PropertiesWithBackingFieldsInsideInlineClass(),
-    AnnotationClassTargetAndRetentionChecker()
+    AnnotationClassTargetAndRetentionChecker(),
+    ReservedMembersAndConstructsForInlineClass()
 )
 
 private val DEFAULT_CALL_CHECKERS = listOf(

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/InlineClassDeclarationChecker.kt

@@ -139,4 +139,24 @@ class PropertiesWithBackingFieldsInsideInlineClass : DeclarationChecker {
             context.trace.report(Errors.DELEGATED_PROPERTY_INSIDE_INLINE_CLASS.on(it))
         }
     }
+}
+
+class ReservedMembersAndConstructsForInlineClass : DeclarationChecker {
+
+    companion object {
+        private val reservedFunctions = setOf("box", "unbox", "equals", "hashCode")
+    }
+
+    override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
+        val containingDeclaration = descriptor.containingDeclaration ?: return
+        if (!containingDeclaration.isInlineClass()) return
+
+        if (declaration is KtFunction && descriptor is FunctionDescriptor) {
+            val functionName = descriptor.name.asString()
+            if (functionName in reservedFunctions) {
+                val nameIdentifier = declaration.nameIdentifier ?: return
+                context.trace.report(Errors.RESERVED_MEMBER_INSIDE_INLINE_CLASS.on(nameIdentifier, functionName))
+            }
+        }
+    }
 }